The field of the invention pertains to athletic shoes and, in particular, to athletic shoes specifically for use in "explosive" sports such as basketball, track and field, volleyball, tennis and soccer.
Modern athletic shoes for sports, in particular sports with explosive movements, are designed and constructed to place the heel significantly higher than the balls of the feet and toes. Typically the slope of the inner sole is at 4.degree. and higher at the heel relative to the ball and toes and thus have a forward slope. Such athletic shoes are constructed in this manner to provide better shock absorption and greater comfort. The forward slope provides a tendency to lift the arch of the foot from the inner sole when braking thus protecting the arch from injury.
However, for certain specific purposes shoes have been disclosed with heel inner soles lower than the inner sole at the ball of the foot and toes. Perhaps the best known example is disclosed in U.S. Pat. No. 3,305,947, the "earth shoe" wherein the heel inner sole is level with or slightly lower than the inner sole at the ball of the foot. This shoe is a walking shoe commercially sold as a sandal with straps and not suited for vigorous athletic activities beyond walking.
U.S. Pat. No. 3,964,181 discloses a shoe to improve the posture of a wearer but nevertheless appear as a conventional shoe. The heel portion is substantially hollowed out to put the heel at 2.degree. -10.degree. reverse slope below the ball of the foot. The inner sole is substantially curved both laterally and longitudinally between the heel and ball of the foot. The preferred slope is 5.degree.. The shoe construction is specifically directed to overcome the sandal appearance and fitting problems of the "earth shoe" design and be applicable to dress shoes and casual shoes such as wing tips, moccasins, brogues and wedges. Thus, this shoe construction is not directed to vigorous athletic activities.
A walking shoe for enhanced exercise is disclosed in U.S. Pat. No. 4,934,073. A reverse slope convex wedge is positioned ahead of the heel and terminating before the heel. The convex wedge also terminates before the ball. Here again, the shoe is not directed to vigorous athletic activities beyond walking. Both of the above walking shoes purposely provide arch support and with such arch support at least a portion of the user's weight is applied through the arch.
A number of devices have been specifically developed for physical therapy that embody a severe reverse slope U.S. Pat. No. 2,769,252 discloses a block affixed to the exterior shoe sole under the ball of the foot and toes. The block creates a severe reverse slope. The shoe construction is to aid in the strengthening of the abdominal muscles by causing an abnormal walking posture. The shoe design clearly would be unsuitable for athletic activities beyond the intended walking exercise.
U.S. Pat. Nos. 3,472,508 and 4,573,678 disclose severe reverse slope devices for exercising the lower leg. Both devices are attached to the feet with straps, the former being intended for feet without shoes and the latter intended for feet in athletic shoes. The former device also provides for an adjustable slope. Both devices are intended for walking with the devices strapped on, however, they are too cumbersome and dangerous for vigorous sports activities.
U.S. Pat. No. 4,526,365 discloses a platform device having a resilient wedge shaped member under the toes and ball of the foot. The wedge creates a reverse slope relative to the heel support of the device. The March 1992 issue of Track & Field News on page 57 refers to platformed spikes by NIKE.RTM. as training and competition shoes having a platform on the front, however, no illustration or detailed explanation is provided.